1. Field of the Invention
This invention relates to digital still cameras, and more particularly to a digital still camera adapted to create zoom image data having a desired zooming magnification depending upon image data held in a video memory and having pixels each having a single image-quality-related element.
2. Description of the Prior Art
In a conventional digital still camera 1 of this kind as shown in FIG. 19, the pixel data of a preceding line, held in a DRAM 2, is temporarily stored into a line memory 3 so that the pixel data of the preceding line and the pixel data of the current line are supplied simultaneously to an interpolating circuit 4. Accordingly, the interpolating circuit 4 performs vertical interpolation based on two pixel data in a vertical direction. The interpolating circuit 4 also includes registers 4a and 4b to hold the preceding-line pixel data in a horizontal direction, and performs horizontal interpolation based on the preceding pixel data and the current pixel data that are simultaneously obtained on each line. Due to this, desired zoom image data is obtainable by the interpolating circuit 4.
In such a prior art, however, a line memory 3 is required to have a memory capacity of 1 line in order to create zoom image data, thus raising a problem of increasing the scale of a circuit.
Therefore, it is a primary object of this invention to provide a digital still camera which is capable of obtaining desired zoom image data while small in memory capacity.
This invention is a digital camera structured to create zoom image data having a desired zoom magnification, comprising: a video memory for holding source image data; a buffer having at least a first capacity corresponding to a data amount of a particular source pixel required to create one zoom pixel; a reading/writing means for reading out of the video memory, and writing into the buffer, pixel data containing the particular pixel at a predetermined clock rate of a reference clock rate multiplied by the number of vertical pixels or more of the particular source pixel; a reading means for reading the pixel data held in the buffer at the reference clock rate; and a creating means for creating pixel data for the zoom pixel based on an output of the buffer.
The buffer has at least a first capacity corresponding to a data amount of a particular source pixel required to create one zoom pixel. The reading/writing means reads the pixel data including a particular source pixel out of the video memory at a predetermined clock rate of a reference clock rate multiplied by the number of vertical pixels or more of the particular source pixel, and write it into the buffer as this. When writing is completed, the reading means reads out the pixel data held in the buffer at the reference clock rate. Then, the creating means creates pixel data for a zoom pixel based on the pixel data outputted from the buffer.
In one aspect of this invention, a first summing means sums up vertical zooming coefficients related to the zoom magnification. A first determining means included in the reading/writing means determines a readout position in the vertical direction of the video memory based on a first summing result by the first summing means.
In one embodiment of this invention, a first determining means extracts a first integer from the first summing result, detects a first difference between the first integer extracted in a previous time and the first integer extracted this time, and renewing the readout position in the vertical direction depending upon the first difference.
In another aspect of this invention, the buffer includes an SRAM having at least a first capacity and accessed on a word-by-word basis, a register for holding predetermined words of pixel data read out of the SRAM. The register is written by the predetermined words of pixel data including the particular source pixel, while the reading means reads the pixel data contained in the vertical direction of the particular source pixel out of the register.
According to another embodiment of this invention, horizontal zooming coefficients related to the zoom magnification are summed up by a second summing means so that the reading means determines a readout position of the register based on a second summing result by the second summing means. That is, the second determining means extracts a second integer from the second summing result, detects a second difference between the second integer extracted at a preceding time and the second integer extracted this time, and renewing the readout position of the register depending upon the second difference.
According to this invention, the pixel data containing a particular source pixel is written into the buffer at a predetermined clock rate of the reference clock rate multiplied by the number of vertical pixels or more of the particular source pixel so that the pixel data held in the buffer is read out at the reference clock rate. Therefore, it is possible to create desired zoom image data while reducing the buffer capacity.